A knowledge of the regulation of gene activity is central to our understanding of the processes of growth and differentiation in normal and malignant cells. Recent evidence suggests that most mammalian cells contain multiple forms of DNA-dependent RNA polymerase that are intimately involved in the regulation of the types and amounts of RNA synthesized in their nuclei. The proposed study is aimed at an investigation of the factors regulating the transcriptional activity and metabolism of the multiple forms of this enzyme in normal and malignant cells. The program calls for the isolation of the major forms of this enzyme from mouse liver and mouse sarcoma 180 ascites cells in sufficient purity for meaningful studies of their structure and metabolism. Many of the analytical and preparative procedures are centered around our method for separating these isozymes by gel electrofocusing. This system allows the simultaneous fractionation of small amounts of tissue and displays in one step and at high resolution the isozymes from crude nuclear extracts. It also has unique advantages as a preparative technique. The subunit composition and structural relationships of the major forms will be investigated by biochemical and immunological procedures. The rates of synthesis and turnover of the isozymes and their constituent subunits will be investigated by tracer studies in vivo in normal mouse organs and in ascites cells produced in the same animals. Attempts will be made to elucidate the molecular mechanisms leading to alterations in the activities of some of the polymerase isozymes at different stages of growth and development and in response to nutritional and hormonal factors.